1. Field of the Invention
This invention relates in general to equipment and methods for chemically analyzing liquid samples, and in particular to equipment and a method for delivering a sample simultaneously to a number of different analytical instruments.
2. Description of the Prior Art
In many industries, various tests must be performed on liquid samples. For example, certain components of military aircraft are made of composite fiber layers. The resins within these composites must be tested for quality assurance. The samples will be prepared in solvents. These samples are then injected into various detecting equipment such as high performance liquid chromatographs (HPLC), size exclusion chromatographs (SEC), gel permeation chromatographs (GPC), and moisture analyzers. Normally individual samples will be prepared and injected separately into each instrument. Quality assurance requirements often dictate that duplicate tests be run.
A disadvantage of this prior technique is that it takes a considerable amount of time to prepare a sample. Even if the sample is prepared by a robotic device, several hours can be required to prepare the sample. After preparation, running the HPLC test itself can take one-half hour or more. Consequently, if numerous samples have to be tested frequently, considerable expense will be involved in labor and equipment to meet the demand.
Proposals have been suggested to split the sample as it is injected into the sample inlet tube. The sample would then run through separate detecting instruments. A disadvantage of this proposal is that splitting of a sample could cause variations in the flow rate. This could cause errors in the analysis. Also, it would require that all analyses use the same solvent system. This would block the use of GPC and HPLC chromatographs at the same time, because these chromatographs often require different types of solvents.
In the detections systems used in the past, injection valves are used. These injection valves have a spool within them that contains a sample chamber and a solvent chamber. Each chamber has an inlet and an outlet. The injection valve has a sample inlet port, a sample excess port, a solvent inlet port and a solvent/sample outlet port. When operating these injection valves, first the sample is injected in through the sample inlet port to flow through the sample chamber and out the sample excess outlet port. A portion of the sample will remain in the sample chamber. Then, the spool rotates to align the sample chamber inlets and outlets with the solvent inlet and solvent/sample outlet ports, respectively. A solvent pump will then push the sample on to the detection units. While this is a workable technique, heretofore it has only been used with a single detection unit